Mechanism of Zr poisoning Al-5Ti-B grain refiners based on the first-principles calculation

ABSTRACT First-principles calculation was carried out to investigate the mechanism of Zr poisoning Al-5Ti-B grain refiners via Ti (or Zr)-adsorbed TiB2 models. The results show that the most energetically favourable sites for both adsorptions of Zr and Ti are bridge- and hollow-sites. The calculated results show that (i) adsorption energy of Ti is slightly more negative than that of Zr; (ii) The adsorption distance of Ti with the interface is shorter than that of Zr; (iii) the number of electric charges acquisition of adsorbed Ti is about twice larger than that of Zr; and (iv) the mixed metallic/covalent bonding on the Ti adsorbed interface is stronger than that on the Zr adsorbed interface. All results exhibit Ti atom is stronger than Zr in the adsorption ability. When both Zr and Ti atom co-exist, the adsorption of Zr on TiB2 weakens the adsorption of Ti. Co-adsorption of Ti and Zr exhibits an atomically roughening interface of TiB2. First-principles calculation of Ti and Zr adsorption on TiB2 well explains the mechanism of Zr poisoning Al-5Ti-B grain refiners in thermodynamic in view of the co-adsorption of Zr and Ti deteriorating the nucleating potency of TiB2 for α-Al.